Hi guys,
Sorry by late reading this thread. I had already compared Xen Source with KVM (and btw, VMware Server 2) in CentOS 5.2 days (2008) for a college job. At this time Xen have more performance than the others, but I'd tested in my desktop: A Core 2 Duo E6420 with 3GB Ram. All the papers I'd used is available in brazilian portuguese, if anyone is interesed I would send. But *IMHO* isn't interesting translating the job to english because, as I said, I did it in CentOS 5.2 (2008) and a *LOT* things has changed in all this hypervisors.
Anyway, here in my job I have two IBMs x3400 (two Xeon 5504 sockets with 8GB Ram and 2 x 160GB [SAS? SATA? I really don't know]) available, and they works perfect with Xen and KVM (both worked as Dom0 before, so we replaced them for rack mounted machines). I really like x86 virtualization, so I can test the hypervisors again in this real servers and write about it in my free time, but I need a metodology to follow up and do a benchmark. (I'm not good in performance metter). If someone else is interesed in do it with me, will be really fun.